Back to EveryPatent.com
United States Patent |
5,293,919
|
Olney
,   et al.
|
March 15, 1994
|
Self-regulating tire pressure system and method
Abstract
A self-regulating tire pressure system and method employs a bistable valve
(10) that allows air from a high pressure reservoir (6) to replenish the
pressure within a tire (4) when it has fallen below an actuating pressure,
and discontinues its operation only after the tire pressure has increased
to a closing pressure that is greater than the actuating pressure. The
system is capable of sensing the valve's (10) frequency of operation as an
indication of a slow tire leak when the frequency exceeds a predetermined
threshold, of sensing the number of valve (10) operations and the duration
of each operation as an indication of a flat tire condition when the
number of operations for a predetermined duration exceeds a second
threshold, and of sensing the duration of the valve's (10) operation as an
indication of a low reservoir (6) pressure condition when that duration
exceeds a third threshold. The valve (10) includes a bistable diaphragm
(94, 120) that receives a reference pressure on one side and the tire
pressure on its opposite side, and snaps between two stable positions
respectively opening and closing the valve (10) in response to the tire
pressure falling below the actuating pressure and then increasing to the
closing pressure.
Inventors:
|
Olney; Ross D. (West Hills, CA);
Reeds; John W. (Thousand Oaks, CA)
|
Assignee:
|
Hughes Aircraft Company (Los Angeles, CA)
|
Appl. No.:
|
793762 |
Filed:
|
November 18, 1991 |
Current U.S. Class: |
152/418; 137/225; 137/554; 152/427; 251/75; 340/448 |
Intern'l Class: |
B60C 023/04 |
Field of Search: |
152/415,416,427,418,429
137/224,225,227,554
340/442,447,448,445
251/75
|
References Cited
U.S. Patent Documents
2213539 | Sep., 1940 | Wiegand | 152/416.
|
2391652 | Dec., 1945 | Stevenson | 152/421.
|
2510052 | Jun., 1950 | Navarro et al. | 137/225.
|
2550986 | May., 1951 | Flanery et al. | 200/61.
|
2939504 | Jun., 1960 | Bedford, Jr. | 152/418.
|
3249916 | May., 1966 | Quinn et al. | 340/445.
|
3602884 | Aug., 1971 | Brumbelow | 340/448.
|
3614732 | Oct., 1971 | Clermont-Ferrand | 340/448.
|
3662335 | May., 1972 | Fritze | 340/448.
|
3665387 | May., 1972 | Enabnit | 340/448.
|
3723966 | Mar., 1973 | Mueller et al. | 340/447.
|
3963887 | Jun., 1976 | Takusagawa et al. | 200/83.
|
4067376 | Jan., 1978 | Barabino | 152/428.
|
4082960 | Apr., 1978 | Denamps et al. | 340/448.
|
4742857 | May., 1988 | Gandhi | 152/418.
|
4938272 | Jul., 1990 | Sandy et al. | 152/427.
|
Foreign Patent Documents |
0305312 | Mar., 1989 | EP.
| |
3209660 | Oct., 1983 | DE.
| |
Other References
Research Disclosure No. 33517, "Low Tire Pressure Signal Apparatus", Mar.
1992.
Communication dated Jun. 3, 1991 from Frank Wiloch (GM Advanced Engineering
Staff) to R. D. Olney (one of inventors of the present invention) relating
to a Low Tire Pressure Monitor.
EPIC Technologies, Inc. brochure, "Technical Description EPIC Low Tire
Warning System", published at least as early as Jul. 1990.
|
Primary Examiner: Ball; Michael W.
Assistant Examiner: Lorin; Francis J.
Attorney, Agent or Firm: Duraiswamy; V. D., Denson-Low; W. K.
Claims
We claim:
1. A self-regulating tire pressure system, comprising:
a wheel for seating a tire, said wheel including a reservoir for providing
a high pressure air source, and
a bistable valve establishing an air flow communication between said
reservoir and a tire seated on said wheel, said valve having a first
stable position in which said valve opens an air flow passageway between
said reservoir and said tire in response to the air pressure within the
tire falling below a predetermined actuating pressure set point, and
having a second stable position in which said valve closes said air flow
passageway in response to the air pressure within the tire increasing to a
predetermined closing pressure set point which is greater than said
actuating pressure set point.
2. The self-regulating tire pressure system of claim 1, said bistable valve
including a reference pressure source and a bistable diaphragm for
receiving said reference and tire pressures on opposite sides of the
diaphragm, said diaphragm having first and second stable positions
respectively opening and closing said air flow passageway in response to
said tire pressure respectively falling below said actuating pressure and
increasing to said closing pressure.
3. The self-regulating tire pressure system of claim 2, said bistable
diaphragm comprising a flexible membrane carrying a first magnetic member,
said valve further comprising a second magnetic member aligned with said
first magnetic member, at least one of said magnetic members being
magnetized to hold said magnetic members together with said diaphragm in
said second stable position when said tire pressure exceeds said closing
pressure, and to allow said diaphragm to flex away from said second
magnetic member to its first stable position in response to said tire
pressure falling below said actuating pressure.
4. The self-regulating tire pressure system of claim 2, said bistable
diaphragm comprising a prestressed diaphragm oriented about a central
plane and having stable positions on opposite sides of said central plane.
5. The self-regulating tire pressure system of claim 4, said reference
pressure source comprising a sealed bellows with an internal pressure
establishing said reference pressure, said sealed bellows bearing against
said diaphragm in opposition to said tire pressure.
6. The self-regulating tire pressure system of claim 4, said reference
pressure source comprising a mechanical spring bearing against said
diaphragm in opposition to said tire pressure.
7. The self-regulating tire pressure system of claim 1, further comprising
means for sensing said valve's frequency of operation as an indication of
a slow tire leak when said frequency exceeds a predetermined threshold,
said means including a secondary winding circuit mounted on the outer
periphery of said wheel and a primary winding circuit mounted on the
vehicle chassis for sensing the reflected impedance of said secondary
winding circuit and a circuit that responds to the reflected impedance
signal from the primary winding circuit to indicate operation of said
valve.
8. The self-regulating tire pressure system of claim 7, further comprising
a logic circuit that responds to the reflected impedance signal from the
primary winding circuit by sensing the number of valve operations and the
duration of each such operation as an indication of a flat tire condition
when the number of said operations for a predetermined duration exceeds a
predetermined threshold.
9. The self-regulating tire pressure system of claim 1, further comprising
means for sensing the duration of said valve's operation as an indication
of a low reservoir air pressure condition when said duration exceeds a
predetermined threshold.
10. The self-regulating tire pressure system of claim 1, for a vehicle
having said wheel mounted with respect to a vehicle chassis, further
comprising sensing means including:
a primary electrical winding on said chassis proximate to said wheel,
means for delivering an alternating electrical signal to said primary
winding to establish a primary winding flux field,
a secondary winding on said wheel within said primary winding flux field,
a valve indicator means connected in circuit with said secondary winding
for varying the secondary winding impedance reflected back to said primary
winding according to whether said valve is establishing said air flow
communication, and
timing means responsive to said reflected secondary winding impedance for
timing operations of said valve.
11. The self regulating tire pressure system of claim 10, wherein said
means for delivering an alternating electrical signal to said primary
winding delivers a pulsed signal with substantially constant current
pulses, and said timing means is responsive to the voltage across said
primary winding.
12. The self-regulating tire pressure system of claim 11, wherein said
means for delivering an alternating electrical signal to said primary
winding delvers a pulsed signal with substantially constant voltage
pulses, and said timing means is responsive to the current through said
primary winding.
13. The self-regulating tire pressure system of claim 10, wherein said
secondary winding and valve indicator means comprising a tuned circuit
with respect to the alternating electrical signal on said primary winding
when said valve is establishing said air flow communication, and said
timing means is responsive to a tuned resonance between said primary and
secondary windings.
14. The self-regulating tire pressure system of claim 10, said means for
delivering an alternating signal to said primary winding delivering a
signal with a duty cycle substantially less than 50%.
15. A self-regulating tire pressure system, comprising:
a wheel for seating a tire, said wheel including a reservoir for providing
a high pressure air source, and
a bistable valve establishing an air flow communication between said
reservoir and a tire seated on said wheel, said valve opening an air flow
passageway between said reservoir and said tire in response to the air
pressure within the tire falling below a predetermined actuating pressure,
and closing said air flow passageway in response to the air pressure
within the tire increasing to a predetermined closing pressure which is
greater than said actuating pressure, said bistable valve including a
reference pressure source and a bistable diaphragm for receiving said
reference and tire pressures on opposite sides of the diaphragm, said
diaphragm having first and second stable positions respectively openings
and closing said air flow passageway in response to said tire pressure
respectively falling below said actuating pressure and increasing to said
closing pressure, said bistable diaphragm comprising a prestressed
diaphragm oriented about a central plane and having stable positions on
opposite sides of said central plane,
said valve including a housing with an inner peripheral recess, said
prestressed diaphragm being lodged in said recess to allow a restricted
movement of said diaphragm within said recess when said diaphragm moves
between bistable positions on opposite sides of its central plane, and
further comprising an air impermeable flexible diaphragm spanning said
housing to block the flow of air therethrough, said flexible diaphragm
being connected to move with said prestressed diaphragm.
16. A self-regulating tire pressure system, comprising:
a wheel for seating a tire, said wheel including a reservoir for providing
a high pressure air source, and
a bistable valve establishing an air flow communication between said
reservoir and a tire seated on said wheel, said valve opening an air flow
passageway between said reservoir and said tire in response to the air
pressure within the tire falling below a predetermine actuating pressure,
and closing said air flow passageway in response to the air pressure
within the tire increasing to a predetermine closing pressure which is
greater than said actuating pressure, said bistable valve including a
reference pressure source and a bistable diaphragm for receiving said
reference and tire pressures on opposite sides of the diaphragm, said
diaphragm having first and second stable positions respectively opening
and closing said air flow passageway in response to said tire pressure
respectively falling below said actuating pressure and increasing to said
closing pressure, said reference pressure source comprising a pressure
regulator for providing said reference pressure from said high pressure
reservoir at a predetermined regulated pressure.
17. A self-regulating tire pressure system, comprising:
a wheel for seating a tire, said wheel including a reservoir for providing
a high pressure air source,
a valve for establishing an air flow communication between said reservoir
and a tire seated on said wheel in response to a low air pressure
condition in the tire, and
means for sensing the timing of operations of said valve as an indication
of the type of low pressure condition,
wherein said valve is a bistable valve having a reference pressure source
establishing a reference pressure and wherein the bistable valve has first
and second set points, said first set point being at a lower pressure than
the second set point, and open and closed positions respectively at first
and second set points for establishing said air flow communication in
response to said tire pressure falling to said first set point, and
breaking said air flow communication in response to said tire pressure
increasing to said second set point.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to self-regulating pressure systems and methods for
vehicle tires, and more particularly to self-regulating systems and
methods in which the tire is automatically replenished from a high
pressure reservoir in response to a sensed low pressure condition in the
tire.
2. Description of the Related Art
Low tire pressure is an important cause of excessive fuel consumption, tire
wear and impaired steerability. A normal tire will typically leak on the
order of 25 percent of its pressure per year due to its inherent
permeability. It is thus good practice to check tire pressure on a regular
basis. However, even checking tire pressure every few weeks may not
prevent these adverse affects when a slow leak is present, and the leak
may go undetected unless a careful record is maintained of how frequently
the pressure in each tire has to be replenished. A fast leak or flat
condition can rapidly cause damage to the tire and even render it unusable
in a short period of time, but this condition may go unnoticed by an
inexperienced driver until it is too late.
It is thus highly desirable to have some mechanism that automatically
replenishes the tire pressure when it is too low, and that warns the
driver of the low pressure condition. One such system is disclosed in U.S.
Pat. No. 4,067,376 to Barabino. This patent incorporates a high pressure
reservoir into the vehicle wheel, and uses a valve that automatically
opens a passageway between the high pressure reservoir and the tire in
response to the tire pressure falling below a selected threshold level.
Operation of the valve also causes a sonic or ultrasonic signal to be
generated which is detected by a sensor mounted in close proximity to the
wheel, typically within the wheel well. When it senses a valve operation,
the sensor initiates a visual and audio warning for the driver. To
differentiate between the different tires, the valve on each tire may be
tuned to generate a signal with a unique frequency, or the sensors for the
different tires may be tuned to detect different components of a uniform
valve signal.
Another system is disclosed in U.S. Pat. No. 4,742,857 to Gandhi. In this
patent the tire valve includes a magnet that moves in response to a
falling tire pressure. Movement of the magnet to a low pressure position
is sensed by a solenoid mounted on the shock absorber adjacent the tire.
The magnetic field from the moveable magnet intercepts the solenoid at
each tire revolution, generating a voltage in the solenoid that varies
with the magnet's position. When the magnet's sensed position indicates a
low pressure condition, a warning is provided to the vehicle operator. If
the operator wishes to replenish the tire pressure, he or she actuates a
switch that supplies current to the solenoid for the appropriate tire. The
solenoid produces a magnetic field that moves its associated magnet to a
position at which a valve from a high pressure reservoir within the wheel
is opened so that air can flow into the tire.
While the above systems can effectively replenish the air pressure within a
tire, they are incapable of distinguishing between normal long term
leakage from a tire, a slow leak condition that requires repair, and a
fast leak or flat tire condition. The vehicle operator is thus uninformed
as to whether a tire repair or replacement is called for. The operator is
also not supplied with any information as to the condition of the high
pressure reservoir, and whether it requires replenishment. Furthermore,
the prior use of separate transmitters within each wheel and associated
receivers on the vehicle requires a power source within each wheel and
complex electronics, and is unduly expensive.
An after market sensor for low tire pressure has been marketed by Epic
Technologies Inc. The sensor monitors tire pressure and causes a radio
frequency (RF) signal to be transmitted in case the pressure falls below a
predetermined set point; transmission of the RF signal actuates a warning
for the vehicle driver. However, the system does not have any mechanism to
automatically replenish the low tire pressure.
SUMMARY OF THE INVENTION
The present invention seeks to provide a new self-regulating tire pressure
system and method that senses a low pressure condition within a tire,
automatically replenishes the pressure to a desired level, is less complex
and expensive than prior approaches, provides the vehicle operator with
information on the cause of the low pressure condition and whether tire
repair or replacement is required, and does not require the intervention
of the vehicle operator to restore tire pressure.
These goals are accomplished with the use of a bistable valve that opens an
air flow between the high pressure reservoir and the tire when the tire
pressure falls below a predetermined actuating level, and halts the air
flow when the tire pressure has increased to a closing pressure that is
greater than its actuating pressure. The valve condition is communicated
to the vehicle by means of a primary winding on the vehicle chassis
adjacent the wheel, and a secondary winding on the wheel that is connected
along with a set of valve contacts in a secondary circuit. The valve
contacts open and close as the valve switches between its two stable
positions, producing a change in the impedance of the secondary circuit
that is reflected back to the primary winding. The reflected impedance
provide an indication of the valve operations.
A logic circuit supplied by the primary winding differentiates between
various low pressure tire conditions. If the frequency of valve operation
exceeds a predetermined threshold, a slow leak as opposed to a normal
pressure loss through the tire wall is indicated. When the duration of the
valve operation exceeds a predetermined threshold, a low reservoir air
pressure condition is indicated. When the number of valve operations that
last for a predetermined duration exceeds a predetermined threshold, a
flat tire situation is indicated.
The valve preferably incorporates a bistable diaphragm that moves between
two stable positions respectively opening and closing the air flow
passageway from the high pressure reservoir. In one embodiment the
diaphragm comprises a flexible membrane that carries a first magnetic
member aligned with a stationary magnetic member. At least one of the
magnetic members is magnetized to hold the two members together with the
diaphragm closing the air flow passageway from the high pressure reservoir
when the tire pressure exceeds the valve closing pressure; the diaphragm
flexes away from the second magnetic member to its other stable position
and opens the air flow passageway when the tire pressure falls below the
valve actuating pressure. In a second embodiment the bistable diaphragm is
a prestressed metal diaphragm that is oriented about a central plane and
has stable positions on opposite sides of that plane. The metal diaphragm
may be lodged in a recess that allows a restricted movement of the
diaphragm when it moves between its bistable positions, thus enhancing the
diaphragm's snap action. In this embodiment an air impermeable flexible
diaphragm may be connected to move with the metal diaphragm, and spans the
housing in which the recess is formed to block the flow of air
therethrough.
The valve compares the tire pressure with a reference pressure that can be
provided from sources such as a pressure regulator, a spring or a sealed
bellows. A flow of air from the high pressure reservoir to the tire is
actuated when the differential between the compared pressures exceeds a
threshold amount.
Further features and advantages of the invention will be apparent to those
skilled in the art from the following detailed description, taken together
with the accompanying drawings, in which:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a portion of a vehicle tire and wheel
illustrating the basic mechanical elements of one embodiment of the
invention;
FIG. 2 is a block diagram of the invention;
FIG. 3 is a diagram of a tire and wheel illustrating their interconnection
through the bistable valve used in the invention;
FIG. 4 is a block diagram showing the communication between the vehicle and
wheel to detect when the valve has operated;
FIG. 5 is a logic diagram of the logic circuitry used to distinguish
between various types of tire leak and low reservoir conditions;
FIG. 6 is a graph comparing the pressure in the high pressure reservoir
with the time required to restore the tire pressure when a pressure
regulator is used to provide a reference pressure for the valve;
FIG. 7 is a sectional view of a bistable valve construction that employs a
pressure regulator;
FIG. 8 is a sectional view of a bistable valve construction that employs
both a pressure regulator and a spring as a combined reference pressure
source;
FIG. 9 is a sectional view of an alternate bistable valve construction that
employs a sealed bellows as a reference pressure source;
FIG. 10 is a graph comparing the pressure in the high pressure reservoir
with the time required to restore the tire pressure when a pressure
regulator is not employed; and
FIG. 11 is a fragmentary sectional view of a valve and high pressure
reservoir incorporated into a conventional wheel.
DETAILED DESCRIPTION OF THE INVENTION
Referring first to FIG. 1, the relevant elements of a vehicle wheel 2 with
a tire 4 seated thereon are illustrated. The wheel 2 includes a built-in
high pressure reservoir 6, with a valve stem 8 extending into the
reservoir so that it can be replenished with pressurized air. The system
is preferably designed to operate with a reservoir pressure of over 100
psi, which is commonly available at most filling stations; 150 psi is
preferred.
A valve 10 provides an air passageway between the high pressure reservoir 6
and the interior of the tire 4. In accordance with the invention, the
valve 10 has a bistable construction such that it opens the passageway
between the high pressure reservoir and tire when the tire pressure has
dropped below a predetermined threshold level, allowing air from the
reservoir to flow into the tire and restore its pressure. The valve does
not close off the passageway until the pressure within the tire has
reached an elevated level that exceeds the original actuating pressure.
For example, the valve may automatically actuate when the tire pressure
falls below about 34 psi, but not reset until the tire pressure has
reached a higher level such as 35 psi.
The opened/closed status of the valve 10 is communicated to the vehicle by
means of a coil of wire 12 installed on the outer periphery of the wheel.
A set of contacts within the valve 10 open when the valve s in one state
and close when the valve is in its other state, and are connected in
series with the winding 12 via a pair of wires 14. The overall winding
circuit is open When the valve contacts are open, and closed when the
contacts are closed.
Mounted on the wheel well 16 of the vehicle chassis approximately
onequarter inch from the wheel windings 12 is a primary winding coil 18
that senses the reflected impedance of the secondary winding circuit 12,
and thus determined whether the valve 10 is open or closed. The primary
and secondary windings 18 and 12 preferably comprise 40 turns of 20 gauge
and 6 turns of 17 gauge solid copper magnet wire, respectively. A pair of
lead wires 20 provide the input to primary winding 18, and also couple the
reflected impedance signal from the primary winding 18 to logic circuitry
described below. Similar connections are made to the primary windings
which communicate with secondary windings on each wheel separately, so
that the status of each tire can be displayed to the operator separately.
FIGS. 2 and 3 show additional aspects of the overall system. The secondary
winding 12 is shown connected in series with pair of switch contacts 22
that are operated by the bistable valve 10, while the primary winding 18
provides a signal to the system's control electronics 24 to indicate the
valve's status. The control electronics sense the frequency and duration
of the valve operations, interpret this data to determine the nature of a
low pressure condition, and actuate the vehicle dashboard display 26 to
notify the vehicle operator of the nature of a problem with any of the
tires, and the identity of the affected tire.
The high pressure reservoir 6 supplies a reference pressure source 28 such
as a pressure regulator; a sealed bellows or a spring can also be used to
establish the reference pressure. The reference pressure source 28
normally has a single set point at which it tries to maintain pressure.
With the addition of the bistable valve 10, a second and lower set point
determined by the valve is added. For example, assume that for an
automobile tire it is desired to begin replenishing the tire pressure when
it drops below 34 psi, and to continue increasing the tire pressure until
it reaches 35 psi. In this situation the reference pressure source 28 does
not begin correcting the tire inflation until the lower set point (34 psi)
is reached. At that time the valve is actuated and allows high pressure
air from reservoir 6 to replenish the tire pressure. When the tire
pressure has been restored back to its normal set point (such as 35 psi)
the valve connection automatically closes, thereby discontinuing further
filling of the tire. The reference pressure provided to the valve for a
150 psi high pressure reservoir 6 may be about 36 psi, for example.
A block diagram of circuitry that is suitable for indicating the valve's
status, and thus whether a leak in the tire is present, is given in FIG.
4. A low duty cycle waveform, preferably with a duty cycle substantially
less than 50%, is generated by an oscillator 30. The waveform is
preferably generated as a series of pulses at a frequency of a few Hz to
about 20 Hz for low power applications, with a pulse duration of about
20-25 microseconds. The pulses operate a circuit driver 32, preferably
implemented as a PNP darlington transistor. The output pulses from driver
32 are fed through the primary winding 18 on the vehicle chassis, and are
coupled thereby to the secondary winding 12.
The impedance of the secondary circuit that includes secondary winding 12
is reflected back to the primary winding 18 to provide an indication of
whether the valve contacts 22 are open or closed, and thus whether the
valve is operating to restore the tire pressure or is quiescent. The
reflected impedance appears as a small load when the contacts are open,
and as a high load when the contacts are closed. This can be implemented
in several ways. One method is to provide constant current pulses to the
primary and look for a reduction in secondary voltage when the contacts
are closed. Another method is to provide constant voltage primary pulses
and look for an increase in secondary current as an indication of closed
contacts. A third method is to connect a capacitor 34 in parallel with the
secondary winding 12 and contacts 22. The capacitor 34 together with the
inductance of secondary winding 12 forms a tuned circuit that oscillates
at a resonant frequency when the contacts 22 are open, but is
short-circuited when the contacts 22 are closed. An open contact
condition, reflecting an operation of the valve, produces a "ringing" or
resonant oscillation when the core of the primary winding 18 has become
saturated and the input pulse turns off.
The waveform reflected back to the primary winding 18 is fed through a
clamping circuit 36 to a zero crossing comparator circuit 38. The
comparator circuit responds to ringing signal by squaring up its edges and
presenting a series of pulses to a counter 40, the operation of which is
enabled when the oscillator 30 is operating by means of a latch circuit 42
fed from the oscillator. The counter 40 functions as a hardware filter,
requiring a fixed number of pulses from the comparator 38 before it
produces an output. For the primary/secondary circuits and drive signal
described above, five input pulses could be required to produce an output
from counter 40. This output triggers a one-shot latch 44 that operates a
driver 46 to turn on a low tire pressure indicator such as light emitting
diode 48 on the vehicle's display panel.
The circuitry of FIG. 4 simply indicates that the bistable pressure valve
has operated, without identifying the tire condition that caused the valve
operation. A logic circuit that responds to the signal reflected from the
secondary winding circuit back to the primary winding by distinguishing
between different low pressure conditions is shown FIG. 5. It utilizes a
clock 50 that generates pulses at a desired rate, such as 1 Hz. The status
of the bistable valve, as indicated by the impedance reflected back to
primary winding 18, is fed from an input line 51 into a two-bit counter 52
that operates by producing a Q1 output over output line 54 the first time
the valve operates, and both Q1 and Q2 outputs respectively over output
lines 54 and 56 the second time the valve operates.
The output of clock 50 and the Q1 output of the two-bit counter 52 are
connected respectively to the clock and enable inputs of a timing circuit
58. The timing circuit determines the time interval between two successive
valve operations. If this interval is less than a predetermined threshold
duration, a slow leak as opposed to a normal long term loss of tire
pressure is indicated. For example, the timing circuit 58 is shown
implemented as an 18-bit counter which produces an output after running
for 262,144 seconds, or approximately 3 days (the 18-bit counter is
fabricated by connecting readily available 14-bit and 4-bit counters in
series). A Q (high) output is produced by counter 58 when it has counted
up to its limit.
The Q2 output of 2-bit counter 52 is connected to a latch 62 that operates
a "slow leak" lamp 64 on the vehicle's dashboard panel. The Q output of
the timing circuit counter 58 is connected through an OR gate 66 to reset
both of the counters 52 and 58; a manual counter reset is also provided
through OR gate 66.
The operation of the FIG. 5 circuit in producing a slow leak warning will
now be described. Assume first that a slow leak is present, causing
successive valve signals to be generated at intervals of less than 3 days.
The first valve signal causes 2-bit counter 52 to enable the operation of
timing circuit counter 58, which begins to count up. The second valve
signal appears before counter 58 has reached its limit. This second signal
activates both the Q1 and Q2 outputs of 2-bit counter 52, which
respectively continue the enablement of timing circuit counter 58 and
provide an input to latch 62, causing the "slow leak" lamp 64 to
illuminate.
Assume next that a second valve operation is not detected before the timing
circuit counter 58 has reached its limit. In this situation the Q2 input
to latch 62 remains low while the timing circuit counter 58 counts all the
way up to its limit, preventing the "slow leak" lamp 64 from lighting. A Q
output is produced by timing circuit counter 58 when it reaches its limit,
causing both the counter 58 and the 2-bit counter 52 to reset. The next
valve signal to be received will thus appear as an initial signal that
enables a restart of the logic circuit operation, with the "slow leak"
lamp 64 continuing to be held off unless an additional valve signal is
subsequently received before the timing circuit counter 58 has counted
out.
While the circuit described thus far in connection with FIG. 5 has been
referred to as a "slow leak" circuit, it does not distinguish between a
slow leak and a fast leak or flat tire situation. A fast leak can be
detected with a similar logic circuit that uses a lower capacity timing
circuit counter, for example an 8-bit counter that lights a "fast leak"
indicator for successive valve operations in less than 4 minutes.
Operation of the "fast leak" detection circuit can be used to lock out the
"slow leak" detector for that tire. Alternately, the manual reset input 68
to OR gate 66 can be used to distinguish a fast from a slow leak. If the
operator observes the "slow leak" lamp, he or she can operate the manual
reset to extinguish the lamp. If it comes on again in a short period of
time, a fast leak is indicated.
Several different tire and high pressure reservoir conditions can be
detected by observing the duration of the valve operations, a capability
that is provided by the present bistable valve approach. To determine the
duration of valve operations, a counter such as 8-bit counter 70 receives
a clock signal from the 1 Hz clock 50, and both enable and reset signals
from the valve input line 51. This configuration causes the counter 70 to
count up when both clock and enable signals are present, and to
immediately reset when the enable signal is removed. Counter 70 determines
the duration of each valve operation. Its seventh and eighth output bits,
respectively Q7 and Q8, are connected as inputs to AND gates 72 and 76,
respectively. The valve signal line 51 is connected as a second input to
both of these AND gates. Thus, AND gate 72 will produce an output when the
Q7 output of output of counter 70 goes high and a valve signal is present,
and AND gate 76 will produce an output when the Q8 output is high and the
valve signal is still present. The Q7 and Q8 counter outputs correspond to
valve operations of 128 and 256 seconds, respectively.
A representative relationship between the air pressure within the high
pressure reservoir and the duration of the valve operation, when a
regulated reference pressure is compared with the tire pressure to actuate
a flow of air from the reservoir to the tire, is illustrated in FIG. 6.
Since air is bled from the high pressure reservoir during each valve
operation, its pressure will progressively decrease for multiple valve
operations, or if one valve operation lasts for an extended period of
time. The reduction in reservoir pressure as a function of the aggregate
time the valve has operated, either as a result of multiple operations or
from a single extended operation, is indicated by curve 78. The rate of
pressure reduction in the reservoir is a function of the initial reservoir
pressure, the valve set point pressures, and the relative volumes of the
reservoir and tire. To provide the operator with an indication that the
pressure within the reservoir has been reduced to a point at which it
should be replenished, a "reservoir low" warning can be provided at a
somewhat arbitrary selected pressure, such as 50 psi. In addition,
extended mobility tires are presently contemplated that can continue to be
operated for up to several hundred miles after a flat has been incurred; a
warning can also be provided if this occurs.
These various situations are indicated in FIG. 6. When the reservoir
reaches an undesirably low pressure, such as 50 psi, the valve operating
time necessary to replenish the tire pressure increases to T1. For a flat
in an extended mobility tire the valve will repeatedly operate, with the
tire gradually losing pressure and the reservoir being further depleted
with each operation; the duration of each operation will remain relatively
constant at T2, until a pressure of about 1 psi is reached (when a 1 psi
pressure differential is used to actuate the valve). Thereafter the valve
will remain open with little or no further replenishment of tire pressure.
Referring back to FIG. 5, a "reservoir low" situation is displayed by a
lamp 78 that is actuated by a latch 80 when both the Q7 and the valve
signals are presented to AND gate 72. To display a flat tire warning, a
3-bit counter 82 connected to the Q7 output of 8-bit counter 70 produces
an output when counter 70 has counted up to Q7 (128 seconds) eight
separate times. This corresponds to eight valve operations of duration T1
(FIG. 6), indicating that the tire pressure has fallen to less than 20
psi. The output of 3-bit counter 82 is delivered through an OR gate 88 to
a latch 90 that lights a "flat tire" lamp 92. The flat tire lamp 92 is
also illuminated by a single occurrence of the Q8 (256 seconds) output of
counter 70, processed through AND gate 76 and OR gate 88. Even if the
3-bit counter 82 has not yet lit the flat tire lamp 92, the occurrence of
a valve operation for 256 seconds or more can be taken as an indication of
a flat tire.
Only a few indicators that may be obtained from the information regarding
valve operating frequency and operating duration have been described.
Numerous other warning indicators that take advantage of the bistable
valve employed by the invention may also be envisioned. It should also be
realized that the assignment of specific times such as 128, 256 or 512
seconds to identify particular situations is somewhat arbitrary, and can
be adjusted as necessary to meet the needs of any particular tire/wheel
system.
One implementation of a suitable bistable valve 10 is shown in FIG. 7. A
flexible diaphragm 94 spans a compartment 96 within the valve housing,
segregating the pressure on one side of the diaphragm from that on the
other side. A permanent magnet 98 is affixed to a striker 99 clamped to
the center of the diaphragm, and is aligned with a bore 100 formed in a
valve end piece 102 of magnetic material. A regulated pressure of say 36
psi is supplied from a pressure regulator 103 to the end piece 102 through
a conduit 104. The pressure regulator 103 is supplied with air from the
high pressure reservoir via a conduit 105, with a branch conduit 106
supplying the same reservoir pressure to the opposite end of the valve
housing. A valve stem 108 on the opposite side of diaphragm 94 from the
end piece 102 receives the reservoir pressure from conduit 106 on one
side, and on its opposite side has an actuating tip 110 that is aligned
with the diaphragm striker 99 within compartment 96. The compartment 96 is
vented to the tire through an outlet 112, and is segregated from the
reservoir pressure of conduit 106 by a flange 114 that retains the valve
stem 108 in place.
The diaphragm 94 thus receives the regulated pressure on its right hand
side, and the tire pressure on its left hand side. The diaphragm, magnet
98 and valve end piece 102 are selected so that the magnet remains seated
against the end piece 102 for a tire pressures greater than the desired
valve actuating pressure. This establishes one of the valve's two stable
conditions. When the tire pressure falls below the actuating threshold,
say 34 psi, the increased pressure differential across the diaphragm
causes it to flex and begin to lift the magnet 98 away from the valve end
piece 102. The magnet's movement away from the valve end piece in turn
reduces the magnetic force of attraction between these two elements, thus
accelerating the movement of the diaphragm to the left. As the diaphragm
continues to travel to the left, but before it reaches it center position,
it pushes against the valve stem's actuating tip 110, opening an air
passageway through the valve stem that allows reservoir air from conduit
106 to flow through the valve stem and outlet 112 to the tire. The valve
stem remains open until the tire pressure has increased to the valve's
second set point, for example 35 psi. At this point the pressure
differential across the diaphragm is reduced to 1 psi, and the residual
magnetic force between the permanent magnet 98 and the magnetic end piece
102 causes the diaphragm to lift off the actuating tip 110, terminating
the flow of air into the tire. Since the diaphragm is now moving towards
the end piece 102 the magnetic attraction between magnet 98 and the end
piece increases, causing the diaphragm to snap over to the right to a
stable off position with the magnet clamped to the end piece 102.
The valve is thus truly bistable, with only two stable positions. In one
position the valve is fully off, with the magnet 98 clamped against the
end piece 102. In the other stable position the valve is fully open, with
the striker 99 depressing the valve stem actuating tip 110.
The metallic end piece 102 and the magnet 98 form the contacts 22 that were
described in connection with FIGS. 2 and 4, and that are connected in the
secondary circuit to indicate whether the valve is open or closed.
Electrical lead wires 116 and 118 are connected respectively to the end
piece 102 and to the metallic striker 99 for this purpose. When the magnet
98 is clamped against the end piece 102 in the position shown in FIG. 7,
the contacts are closed and the capacitor 34 of FIG. 4 is short-circuited,
thus preventing a ringing in the secondary circuit and providing an
indication that the valve is off. When the diaphragm has flexed to the
left and is depressing the valve stem actuating tip 110, the magnet 98 is
electrically isolated from the end piece 102; this opens the contacts 22
of FIG. 4 and produces a resonant LC secondary circuit that indicates the
valve is operating.
It is important that the valve have no stable position other than fully
open or fully closed, so that it will not continuously supply a small
steady air flow to a slow leak without cycling. Another valve arrangement
that can also be used for this purpose is illustrated in FIG. 8. Several
elements of this embodiment are the same as for the valve of FIG. 7, and
are identified by the same reference numerals. In the embodiment of FIG. 8
a prestressed metal diaphragm 120 has a peripheral lip 122 that is clamped
to the valve housing so that the diaphragm spans the interior of the
housing. An air impermeable flexible diaphragm 124 spans the housing
adjacent to the metal diaphragm 120, with its periphery clamped in place
so that air cannot flow from one side of the rubber diaphragm to the
other. The tire pressure is introduced into the compartment 96 on the
valve side of the air impermeable diaphragm 124, while regulated pressure
from the pressure regulator (not shown) is introduced into a spring
compartment 126 on the opposite side of the metal diaphragm 120 through an
inlet port 127, and high pressure air from the reservoir is introduced to
a high pressure area 128 at the valve inlet. A metallic connector 129
clamps the middle sections of the two diaphragms and forces them to flex
together. An electrical connection is made to the valve stem tip 110
through the valve stem 108 via a metal collar 130 around the valve stem
and a lead wire 131 that extends through a feed-through bushing 132 in the
housing wall. An electrical connection is made to the metal diaphragm 120
with a lead wire 134 that connects to the valve housing at any convenient
location. Lead wires 131 and 134 are connected in series with the
secondary winding on the wheel.
A coil spring 136 is lodged within the spring compartment 126 between a lip
on the metallic connector 129 and the opposite end of the spring
compartment 126. The spring 136 provides a reference pressure that opposes
the tire pressure on the opposite side of the diaphragms 120 and 124 to
control the valve operation. While the spring 136 might be used as the
sole source of reference pressure, the spring force tends be unevenly
distributed across the metal diaphragm 120, and the magnitude of the
spring force varies with the diaphragm position. These drawbacks are
mitigated with the addition of the regulated air pressure within the
spring compartment 126, which supplies an evenly distributed pressure to
the diaphragm that does not vary with the diaphragm position. When the
regulated pressure is used together with the spring to provide a reference
pressure the spring pressure may be correspondingly reduced, such as to
about 20 psi.
In the position shown in FIG. 8, the dome of the prestressed metal
diaphragm 120 is flexed to the left to depress the valve stem tip 110 and
actuate the valve stem. High pressure air thus flows into the tire until
the tire pressure has increased to the desired second set point, at which
time the reduced pressure differential across the diaphragm causes it to
snap to its second stable position (indicated by a dashed line), with its
dome flexed to the right away from the valve stem. The two lead wires 131
and 134 are electrically connected when the diaphragm 120 is flexed
leftward to actuate the valve, and electrically separated when the
diaphragm is flexed rightward to shut the valve off. The making and
breaking of these contacts provides an indication of the valve status, in
a manner similar to (but out of phase with) the contacts of FIG. 7.
The prestressed metal diaphragm 120 has only 2 stable positions, with its
dome flexed either left or right as indicated in FIG. 8. The metal
diaphragm is preferably formed from 0.005 inch thick stainless steel, 1.25
inch in diameter with a 0.04 inch high dome.
Another valve embodiment that employs a different source of reference
pressure is illustrated in FIG. 9. In this embodiment a sealed bellows 138
is filled to the desired reference pressure, such as 36 psi. A bistable
metal diaphragm 140 similar to the diaphragm 120 of FIG. 8 has its center
connected to move with the bellows 138 between valve actuating and valve
non-actuating positions. As shown in FIG. 9, the diaphragm 140 has a
central opening that is mounted on a striker 142 affixed to the bellows.
When flexed to the right as shown, the valve stem 108 is not actuated.
When the tire pressure outside the bellows drops below the valve actuating
point, the reference pressure within the bellows causes the diaphragm to
snap to the left, depressing valve stem tip 110 to actuate the valve. This
permits high pressure reservoir air from the left side of the valve stem
108 to flow through the valve and out to the tire. The position of the
valve is monitored by the lead wire 131 connected to the valve stem tip
110 as in FIG. 8, and by a second lead wire 144 that is either connected
to the striker 142 through a metallic bellows end plate 146, or through
the metallic diaphragm 140 in the valve housing if a good electrical
connection is maintained between these two parts.
The prestressed metal diaphragm 140 is similar to the diaphragm 120 of FIG.
8, but it is shown lodged within an inner peripheral recess 148 formed in
the wall of the valve housing. The diaphragm thickness is less than the
width of the recess, allowing the diaphragm to "float" axially within the
recess. This adds to the diaphragm's snap action when it moves from one of
its stable positions to the other.
A generalized curve that relates the pressure in the high pressure
reservoir to the valve operating time required to replenish the tire
pressure, for a valve in which a sealed bellows or a spring but not a
regulated pressure is used as a reference for the tire pressure, is
illustrated in FIG. 10. Since the pressure supplied by a sealed bellows or
spring reference will not fall below its predetermined set point, even
when the pressure in the high pressure reservoir falls below that set
point as a result of repeated valve operation, the valve will be
permanently actuated once the high pressure reservoir falls to the
pressure st point for resetting the valve after an operation. This is
indicated in FIG. 10 by a flattening of the curve so that it becomes
horizontal once the illustrative set point of 35 psi is reached. Even
through the reservoir pressure will fall below 35 psi if the tire
continues to leak, the reference pressure will remain at its preset level,
such as 36 psi. For this type of valve the flat tire warning logic of FIG.
5 will not be applicable, although the other warnings shown in FIG. 5 can
still be provided.
FIG. 11 shows the valve of FIG. 9 incorporated into a wheel 2. A mounting
plate 148 is welded across two existing sections of the wheel rim, with
the valve 150 carried by the mounting plate within a space between the two
wheel sections. Additional plates 152 and 154 are welded across contours
around the periphery of the wheel to form reservoir sections that are
interconnected by drilled openings 156. The primary winding 18 is shown
wound around a core 158, with the processing electronics mounted on a
substrate 160 inside a molded polyurathane housing 162. The invention can
thus be incorporated into a standard wheel, although customized wheels may
also be provided.
A tire pressure regulating system and operating method that provides
detailed information on the exact condition of the tire, and is both
simple and inexpensive in construction, is made possible with the
invention. While several illustrious embodiments of the invention have
been shown and described, numerous variations and alternate embodiments
will occur to those skilled in the art. For example, the valves described
herein will have applications outside of tire pressure regulation, and the
secondary winding contacts can be operated normally closed rather than
normally open. Such variations and alternate embodiments are contemplated,
and can be made without departing from the spirit and scope of the
invention as defined in the appended claims.
Top